A gas turbine is an apparatus that converts thermal energy of high-temperature combustion gas into rotational energy and takes out the converted energy as electric power, and turbine blades incorporated in the gas turbine are always used in the high-temperature combustion gas. Accordingly, the turbine blades each include cooling flow channels such as serpentine flow channels, and take in cooling air from the outside to thereby cool a blade shape portion thereof. In particular, a fillet portion forming a joint surface between the blade shape portion and the platform of each turbine blade has a thicker wall and thus is difficult to cool. Hence, the wall temperature of the fillet portion is relatively high, and the fillet portion tends to be subjected to a high thermal stress, in terms of a thermal load and a blade structure. A thermal stress tends to increase particularly in the fillet portion near the leading edge and a portion on the pressure side (positive pressure side) of the blade shape portion near the leading edge. In order to solve this problem, various methods of cooling the fillet portion by convection cooling have been proposed as means for cooling the fillet portion of the turbine blade.
Japanese Unexamined Patent Application, Publication No. 2006-170198 discloses the following solution. A branch pipe of cooling air is drawn from a cooling air supply channel provided in a blade shape portion, a film cooling hole is opened so as to pass through a fillet portion, and the cooling air is blown out from the film cooling hole, to thereby cool the fillet portion.
Japanese Unexamined Patent Application, Publication No. 2008-202547 discloses the following cooling means. A plurality of cooling air pipes are branched off from a cooling air supply channel of a blade shape portion, are extended below a fillet, and are connected to a platform surface. Cooling air passes through the cooling air pipes to be blown out from a film hole on the platform surface.